8:00 PM PT: A hospital spokesperson tells TMZ, Heather was awake and responsive when she arrived today -- and she is currently responding well to treatment. According to the spokesperson, Heather is doing much better now and doctors are hopeful she will be released tomorrow.

We're also told Heather's parents are currently with the actress inside the hospital.

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Heather Locklear was taken to the hospital by ambulance Thursday afternoon after taking a dangerous mix of prescription drugs and alcohol ... law enforcement sources tell TMZ.

We've learned ... Locklear's sister called 911 at 2:05 PM PT fearing Heather was in danger.

The fire department, along with the Ventura County Sheriff's Department responded. Paramedics examined Heather and determined she needed to be hospitalized.

This is not the first time Locklear has had a medical emergency where 911 responded. In 2008, her doctor was concerned she may have overdosed on prescription meds. He called 911 and the operator described the situation as a "suicide attempt." It turned out to be a false alarm.

Locklear recently called off her engagement to Jack Wagner.

Heather was at the Lakers game Tuesday night ... hanging with a friend, who was playfully trying to take away her beverage. It's unclear if the drink contained alcohol.